Picked up an old nitro trainer secondhand and got it running again

I had a similar headache when I picked up an older fiberglass warbird setup last winter. It wasn't a glow engine, but the complexity of the existing servos and receiver wiring felt like a tangled mess. My biggest struggle wasn't the mechanical tear down, which was rough, but getting the control surfaces to respond consistently after replacing the actuator gears. They were skipping slightly til I adjusted the linkage by just a couple of millimeters. Once I got the system humming, the real challenge was the propeller pitch. The original owner had installed a very aggressive prop that was suitable for climbing but made the low-speed glide feel jittery. I ended up trying a smaller diameter propeller with a slightly lower pitch rating, and the handling became much smoother during the initial checks in the yard. That little change made all the difference in how the plane felt under manual input.

It sounds like you are in a good spot once the bench firing is solid. Remember that even with perfect mechanical prep, the stability of the airframe itself dictates a lot of the initial flight characteristics. If the wing profile is slightly off from the original design, you might experiance some unexpected yaw at lower speeds. I spent several hours just adjusting the trim tabs before I ever committed to a full throttle run.

I usually go for the airframe check right after getting the powerplant back together. It sounds minor, but if the old plastic or wood frame has suffered even small stress cracks from years on the ground, you are going to get immediate trouble once you put power to it. I picked up an old trainer last year for almost nothing and the fuselage near the wing roots had hairline fractures. They were barely visible unless you ran a bright light over them. When I got it, I spent a good hour just running my finger along every seam and strut connection, specifically looking at the areas where the landing gear mounts were located. I also replaced the main propeller, which was bent and chipped from being stored improperly. Getting the prop nut tightened correctly is huge; you do not want that piece vibrating itself off while you are trying to get some air time. It takes time to find all that hidden damage, but skipping that inspection usually ends up being much more expensive than the hour you spent checking the joints. Glad your engine started up, that is always the best feeling.

$50 for a running trainer is a steal, nice grab. I did the same thing last summer with an old glow plane that had been sitting in someone's attic. The varnish thing is real, had to soak my carb overnight in denatured alcohol to get it clean. Sim time will pay off big, that's how I learned. One thing to watch, those old trainers can be nose heavy if the previous owner added weight for some reason. Check the balance point before your first flight, makes everything way easier.

Good on you for doing the sim time first, that habit saves more airframes than anything else. One thing I'd check before the maiden that nobody thinks about until the plane's in the air: the tank placement. On those old trainers the fuel tank was often relocated or the foam inside crumbled, and if it's not sitting right at the balance point the engine runs lean mid flight when the fuel drops. Also give the nose seal a look, an old glow engine that sat for years can have a dried crank seal that'll make tuning a nightmare at the field even if it fires fine on the bench with a full tank.

Quick update — I went ahead and did the airframe check like one person mentioned. There was a small structural crack near the wing spar that needed filling, which helped alot. However, I'm still trying to figure out the correct servo throws to get the control surfaces moving smoothly. Does anyone have a go-to setting for a small trainer build like this?